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Accuracy Questions


teadams
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For the past several years I have been using the Nuvi 500, which has a geocaching mode, to both find and place geocaches. This past week I placed yet another cache, doing as I always did, visit the location several times and save a waypoint for future use. On the first 2 trips I'd walk a short way away then return and after standing in the future cache location save yet another waypoint. On my third trip I used the average location of the previous locations and it showed me to be 1 1/2 feet away when I was standing at the cache site.

This week I bought a new Montana 600 to replace the Nuvi for caching and this morning I walked out to this new cache location. BTW, this caches has been found by one user during a snow storm and his GPS reading was jumping around a quite a bit.

 

When I got to the cache, my Montana showed the programmed location to be ~30 feet away! Hence my following questions -

1) Has the technology improved so much that the old Nuvi 500 is less accurate then the newer Montana?

2) Should I update the cache location to the new reading I got this morning?

3) Is there perhaps a setting on the Montana that I might have missed to improve the accuracy?

4) should I just wait till more people find the cache and see what they have to say about the accuracy?

5) for Montana 600 owners - What sort of accuracy are you typically seeing?

 

Thanks

Tim

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A discrepancy of 30' is not unusual and can be caused by several factors including different satellite constellations between the two readings. If I were you , I would use the waypoint averaging function on the Montana. Let it run until it shows a high confidence level (95% to 100%), then save and trust the averaged waypoint coordinates. If you want to increase the accuracy further, go back and re-average on a different day.

Edited by alandb
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A discrepancy of 30' is not unusual and can be caused by several factors including different satellite constellations between the two readings. If I were you , I would use the waypoint averaging function on the Montana. Let it run until it shows a high confidence level (95% to 100%), then save and trust the averaged waypoint coordinates. If you want to increase the accuracy further, go back and re-average on a different day.

 

Exactly.

 

Return to the same location on multiple days, at different times of the day, and re-average the same waypoint each time, with the waypoint averaging application.

 

I would believe the Montana reported GPS position to be more accurate than a nuvi.

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As already noted: 30' off is fully normal - even with a modern receiver. Albeit with a completely free view of the sky and optimal reception conditions it would be a little higher than expected.

 

As for "3) Is there perhaps a setting on the Montana that I might have missed to improve the accuracy?": If you are in an area that can make use of the WAAS/EGNOS system, enable that setting in the receiver.

 

The montana is probably more accurate than the nuvi. Car GPS often have puny antennas.

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Despite its quirks, I believe the Montana is very accurate. In good conditions, I typically get down to 5-20 feet when navigating to a cache, and it usually picks one spot for ground zero and sticks with it, doesn't float too much unless the conditions are tough. On the occasion I happen upon a cache with a difference of over 35-40 feet, when not attributable to conditions, I would tend to believe it was not placed accurately, or placed with a much older unit (such as nuvi 500 or pre-high sensitivity/WAAS receivers)

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